PLC preformance Q ?

[JIMCON]

Hello..

I am right now comparing two Siemens PLC CPU´s. (s5 and S7 CPU)
But just to be sure I wonder what data is the most crucial information of importance when i want to know the CPU´s performance ?

When im comparing two systems I look on Execution times and so on..

Examplewise : I have an S5 944CPU that i want to replace and the result i get from my reasearch for 300 and 400 is S7 317-2DP CPU and my reslut on a S7 400 is a 414-2 CPU.. Can this be correct ? im very unsure..

 

[jacekd]

With boolean operations 317 and 414 are comparable. But when it comes to arithmetic 414 is much faster.

 

[SimonGoldsworthy]

Don't forget that you need to consider the size of the program and the I/O space as well.

 

[JesperMP]

That is an interesting question.
How "big" an S7 CPU does one need in order to replace an S5 CPU ?

I just checked the instruction times for a S5-944, an S7-315, an S7-317 and an S7-414. I checked only the execution times for a boolean "AND", Load and transfer of a dataword, and addition of an integer.

 

CPU    944    315       317         414

A      0.8    0.1..0.3  0.05..0.06  0.06

L DW   1.7    1.8       0.24        0.12

T DW   1.4    1.6       0.30        0.075

+ I    0.8    0.6       0.2         0.06

It looks like the 315 is the closest one to the 944 !
The others are much faster.

I didnt check or consider floating point math, as you are upgrading from a S5-944.

I also did not check how much i/o each CPU can handle, or how much memory there is.
But I am sure that the 512kB on the 317 will be more than enough to replace the program in the 944.

 

[JIMCON]

Ok Thank you all for the answers and help..

This is very intressting 315-2DP is the closest... But im abit unsure about if it can handle my kommunikation. I have 2 modbus cards for 2 HMIs, 1 FMS card to 4 Other Controllers and a DP card to 13 I/O nodes.
I dont know exact how many bytes each connection are processing..

 

[Terry Woods]

You didn't seem to get the point...

The 315 is the closest to the 944 only in that it is nearly as slow as the 944.